Electrochemistry method having improved efficiency and associated electrochemical reactor such as a high temperature electrolyser (eht)

ABSTRACT

An electrochemistry method to produce a reaction gas of a lesser molar mass than that of an initial constituent of gas or vapor, according to which the gas or vapor of the initial constituent is made to flow, and the reaction gas is recovered in the path in which the initial constituent is made to flow. At least one vortex is created in a zone upstream from the reaction gas recovery zone, wherein the vortex can separate the produced reaction gas from the initial constituent still present to subject the initial constituent to an electrochemical process in the upstream zone. In a high-temperature water electrolysis application according to the method, by the vortex, the produced hydrogen is separated from the surplus steam to subject the surplus stream to an electrolytic process within the electrolyser itself.

TECHNICAL FIELD

The invention concerns an electrochemistry method to produce a reactiongas of a lesser molar mass than that of the initial constituent(s) inthe form of gas or vapour, according to which the gas or vapour of theinitial constituent(s) is made to flow, and the reaction gas isrecovered in the path in which the initial constituent(s) is/are made toflow.

It relates to the improvement of the efficiency of such a method.

The principal application with which the invention is concerned iselectrolysis of water at high temperature (EHT), also calledhigh-temperature steam electrolysis (EVHT).

PRIOR ART

An electrochemical reactor includes multiple elementary cells formed bya cathode and an anode separated by an electrolyte, where the elementarycells are electrically connected in series by means of interconnectingplates which are generally interposed between an anode of an elementarycell and a cathode of the next elementary cell. An anode-anodeconnection followed by a cathode-cathode connection is also possible.The interconnecting plates are electronic conducting components formedby one or more metal plate(s). These plates also provide the separationbetween the cathodic fluid flowing in one elementary cell from theanodic fluid flowing in a following elementary cell.

The anode and the cathode are made of a porous material through whichthe gases can flow.

In the case of electrolysis of water to produce hydrogen at hightemperatures, steam flows in the cathode where the hydrogen is generatedin gaseous form, and a draining gas can flow in the anode, and by thismeans collect the oxygen generated in gaseous form at the anode. Mosthigh-temperature electrolysers use air as the draining gas in the anode.

At the current time the fluid circuits produced by the compartmentsdelimited by the interconnecting plates have a relatively simplearchitecture.

As a general rule the fluid at the outlet of the cathode includes notonly hydrogen which it is sought to produce, but also surplus steam leftover from the electrolysis electrochemical reaction itself. In otherwords, the conversion rates of high-temperature electrolysers are not100%. Indeed, to favour an average production density, steam is usuallydeliberately produced in excess quantities, which occurs to thedetriment of the attaining of a high rate of steam consumption (or highhydrogen conversion rate).

After this, when it is desired to come close to a 100% conversion ofsteam into hydrogen, it has hitherto appeared necessary either tooversize the surface of the cells, or to optimise the distribution ofthe fluids over the surface such that, whatever the path followed by thesteam from its inlet, the passage time is roughly the same. Adisadvantage of the first option is a reduction of average production,whereas a disadvantage of the second option is an implementation (thesteam circuit which must be manufactured) which may be complex.

In addition, many designers of EHT electrolysers tend, from the designstage, to pay particular attention to the level of density of productionto be attained, to the detriment, therefore, of the conversion rate, asset out above.

Lastly, in respect of these same designers, it is easy at the outlet ofthe cathode to separate the unconverted steam from the hydrogen producedby, for example, installing additional means downstream and outside thehigh-temperature electrolyser, where the function of these additionalmeans is to separate the remaining steam from the hydrogen produced. Inmost designs of electrolysers which are currently manufactured theseadditional means are constituted by condensers fitted outside theelectrolysers to separate the water from the hydrogen. Selective porousmembranes have also been mentioned as additional means, also fittedoutside the electrolysers, which allow the hydrogen to pass throughpreferentially, compared to the steam.

The disadvantages of high-temperature electrolysers according to thestate of the art, as described above, can therefore be summarised asfollows: their efficiency is not perfect due to the fact that steamremains at the outlet, and their operation requires the use ofadditional downstream means to separate the hydrogen produced from thesteam left over from the electrolysis reaction itself.

One aim of the invention is therefore to compensate for all or some ofthe disadvantages of the prior art, and therefore to propose a solutionwhich at least enables the hydrogen production efficiency to be improvedin a high-temperature electrolyser.

A more general aim of the invention is to propose a solution whichenables the efficiency of an electrochemistry method to be improved witha view to producing a reaction gas of lesser molar mass than that of theinitial constituent(s) in the form of gas or vapour, according to whichthe gas or vapour of the initial constituent(s) is made to flow, and thereaction gas is recovered in the path in which the initialconstituent(s) is/are made to flow.

DESCRIPTION OF THE INVENTION

To accomplish this, one aim of the invention is an electrochemistrymethod to produce a reaction gas of lesser molar mass than that of theinitial constituent(s) in the form of gas or vapour, according to whichthe gas or vapour of the initial constituent(s) is/are made to flow, andthe reaction gas is recovered in the path in which the initialconstituent(s) is/are made to flow, characterised in that at least onevortex is created in a zone upstream from the reaction gas recoveryzone, where the vortex is able to separate the produced reaction gasfrom the initial constituent(s) which is/are still present, in order tosubject the latter to an electrochemical process in the said upstreamzone.

It is self-evident that a zone upstream from the reaction gas recoveryzone must be considered in the broad sense as being a reaction zone inwhich the transformation from steam to hydrogen takes place.

Thus, the invention essentially consists in slowing the output of theinitial constituent(s) compared to the gas derived from the reactionwhich, since it is less dense, will be able to be output directly,whereas the initial constituent(s) will be ejected tangentially towardsthe outside of the vortex, and therefore be subjected once again to anelectrochemical process in the zone upstream from the outlet.

From one standpoint the invention relates to a method ofhigh-temperature electrolysis of water according to the method describedabove, and implemented by at least one elementary electrolysis cellformed of a cathode, an anode and an electrolyte inserted between thecathode and the anode, according to which steam at least, in contactwith the cathode, is made to flow from an inlet end to an outlet end,through which end the produced hydrogen is recovered, and according towhich at least one vortex is created in a zone upstream from the outletend, where the vortex/vortices is/are able to separate the producedhydrogen from the steam which is still present in order to subject thelatter to an electrolytic process in the said upstream zone.

According to the invention, means to create a vortex are thereforeincorporated into the high-temperature electrolyser itself, whichtherefore favour the output of the hydrogen, and which slow the outputof the steam by ejection to outside the vortex.

The creation of a vortex (or swirl) enables high centripetalaccelerations to be attained, and therefore centrifugal forces to beexerted, of different intensities depending on the species. The term“high temperatures” is understood to mean, in the context of theinvention, temperatures at least equal to 450° C., and typically ofbetween 700° C. and 1000° C.

Due to this integration it is possible to envisage manufacturing ahigh-temperature electrolyser (EHT) with an inlet for steam and a singleoutlet for the produced hydrogen, since the surplus steam in thevicinity of the outlet is once again transformed into hydrogen. Anelectrochemical reactor for electrolysis of water thus completelytransforms the steam provided at the inlet, provided that the steamremains for a sufficiently long time. Therefore, by creating one or morevortices, the water molecules will be kept for a longer period in theactive electrochemical reaction zone by centrifugation; and they willhave an increased possibility of being transformed into hydrogen.

The electrolysis of water concerned by the invention is preferablyaccomplished at temperatures of between 700° C. and 1000° C.

Advantageously, in order to improve performance, i.e. theelectrochemical efficiency, multiple vortices in parallel or in seriesrelative to one another are created in the zone upstream from the outletend.

Each vortex is preferably created with a tangential speed at least equalto 80 m/s, and preferably greater than 100 m/s.

Also preferably, each vortex is created such that it is possible toobtain an acceleration of greater than 10⁶m/s².

The invention also concerns an electrochemical reactor, intended toproduce a reaction gas of lesser molar mass than that of the initialconstituent(s) in the form of gas or vapour, including a stack ofelementary electrochemical cells, each formed from a cathode, an anodeand an electrolyte inserted between the cathode and the anode, where atleast one interconnecting plate is fitted between two adjacentelementary cells and in electrical contact with one electrode of one ofthe two elementary cells and one electrode of the other of the twoelementary cells, where the interconnecting plate delimits at least onecathodic compartment and at least one anodic compartment for the flow offluids respectively at the cathode and at the anode, characterised inthat it includes means to create at least one vortex in a zone upstreamfrom the outlet end of the cathodic compartments and/or of the anodiccompartment, where the vortex/vortices is/are able to separate theproduced reaction gas from the initial constituent(s) which is/are stillpresent, in order to subject the latter to an electrochemical process insaid upstream zone.

The means to create the vortex/vortices advantageously consist of holespierced in the at least one interconnecting plate upstream from theoutlet end of the cathodic compartments. This solution is simple toimplement and can be applied easily in all types of interconnectingplates.

With the habitual flow rates found in an EHT electrolyser and thedimensions of the cells of electrolysers, the diameter of the holes ispreferably less than 1 mm.

Lastly, the invention concerns a plate, intended to be used as aninterconnecting plate in a reactor as described above, consisting of anassembly of two partially buckled plates forming dished recesses in theform of grooves, where the assembly includes at least one aperture, eachof which traverses both assembled metal plates, and made in adifferently dished zone at the end of the grooves, and holes traversinga single one of both metal plates, also made in the differently dishedzone at the end of the grooves, and where the holes are distributed onthe periphery of the aperture; where the diameter of the holes is of theorder of 1 mm or less, and the assembly of both metal plates in thedifferently dished zone delimits a passage between the two metal plates,and between the holes and the aperture on the periphery of which theyare made.

There is preferably an even number of holes. By this means alternaterotation of the vortices is favoured.

Again preferably, the end of the grooves are made such that a gas jet orblend of gas and vapour is created in the said end, where the jet alsohas an outflow tangential to one of the holes. The vortices phenomenonis favoured by bringing about the jet tangentially in this manner.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Other characteristics and advantages will be seen more clearly onreading the detailed description made with reference to the figures,among which:

FIG. 1 is a side view of an embodiment of a reactor for high-temperatureelectrolysis according to the present invention,

FIG. 5 is a section view of the reactor in FIG. 1 in plane A-A,

FIG. 1B is a section view of the reactor in FIG. 1 in plane B-B,

FIG. 2 is a top view of an interconnecting plate according to theinvention used in a reactor for high-temperature electrolysis,

FIG. 2A is a detailed section view of FIG. 2 along axis A-A,

FIG. 3 is a diagrammatic representation of the physical phenomenonaccording to the invention,

FIG. 4 is a graph of the change of average production as a function ofthe flow rate of the steam at the inlet, of an EHT electrolyseraccording to the state of the art, and according to the invention,respectively.

DETAILED ACCOUNT OF PARTICULAR EMBODIMENTS

The invention is described in relation to a type of architecture ofhigh-temperature water electrolyser to generate hydrogen. It isself-evident that the invention can be applied to other architectures,and also to other chemical or electrochemical reactors, in which thereis, firstly, a reaction product which is less dense than the initialproduct(s), where the transformation reaction requires time “andreconcentration”, and where the device can be inserted into it. The hightemperatures at which the represented electrolyser operates are between700° C. and 1000° C.

It is stipulated that the terms “upstream” and “downstream” are usedwith reference to the direction of flow of the steam and of the hydrogenproduced at the cathode.

It is stipulated that the representations of the different elements arenot to scale.

In FIG. 1 an EHT electrolyser according to the present invention hasbeen represented, including multiple stacked elementary cells C1, C2,etc.

Each elementary cell includes an electrolyte positioned between acathode and an anode.

In the remainder of the description we shall describe cells C1 and C2and their interface in detail.

Cell C1 includes a cathode 2.1 and an anode 4.1 between which ispositioned an electrolyte 6.1, for example a solid electrolyte,generally 100 μm thick in the case of cells called “electrolyte support”cells and several μm thick in the case of cells called “cathode support”cells.

Cell C2 includes a cathode 2.2 and an anode 4.2 between which anelectrolyte 6.2 is positioned. All the electrolytes are of the solidtype.

Cathodes 2.1, 2.2 and anodes 4.1, 4.2 are made of a porous material andare, for example, more than 500 μm thick, typically the order of 1 mmand 40 μm respectively.

Anode 4.1 of cell C1 is connected electrically to cathode 2.2 of cell C2by an interconnecting plate 8 which comes into contact with anode 4.1and cathode 2.2. In addition, it allows anode 4.1 and cathode 2.2 to bepowered electrically.

An interconnecting plate 8 is interposed between two elementary cellsC1, C2.

In the represented example it is interposed between an anode of anelementary cell and the cathode of the adjacent cell. But it could beinterposed between two anodes or two cathodes.

Interconnecting plate 8 defines, with the adjacent anode and adjacentcathode, channels through which fluids flow. More specifically, theydefine anodic compartments 9 dedicated to the flow of the gases in anode4 and cathodic compartments 11 dedicated to the flow of the gases incathode 2.

In the represented example an anodic compartment 9 is separated from acathodic compartment 11 by a wall 9.11. In the represented example,interconnecting plate 8 also includes at least one duct delimiting, withwall 9.11, anodic compartments 9 and cathodic compartments 11.

In the represented example the interconnecting plate includes multipleducts 10 and multiple anodic compartments 9 and cathodic compartments11. Advantageously, duct 10 and the compartments have hexagonalhoneycomb sections, which enables the density of compartments 9, 11 andducts 10 to be increased.

As represented in FIG. 1A, steam is circulated in each cathode 2.1, 2.2.

Arrows 12 of FIG. 1A thus clearly represent the path in the anodiccompartments 9 and cathodic compartments 11.

As represented in FIG. 1B, the architecture of the electrolyser alsoenables first end 10.1 of duct 10 to be connected to a supply of steamvia another unrepresented duct, and second end 10.2 of duct 10 to beconnected to cathodic compartment 11. Arrow 14 thus shows the returnflow of the steam from its flow in duct 10 (arrow 16) towards cathodiccompartment 11.

It may be decided to cause a draining gas to flow in anodic compartments9 to evacuate the oxygen (see arrows 13). Arrows 12 and 13 of FIGS. 1Aand 1B thus clearly represent the simultaneous path in anodiccompartments 9 and cathodic compartments 11. It is self-evident that inthe context of the invention the represented flow can equally be sorepresented in the other direction (arrows 12 and 13 in the oppositedirection).

The inventor found that at the outlet end of each cathode steam blendedwith the produced hydrogen remained: this steam is therefore left overfrom the electrolysis reactions which took place upstream.

It is known to treat this surplus steam by separating it from theproduced hydrogen, most often by means of condensers fitted downstreamfrom the electrolyser.

The inventor then had the idea of creating one or more vortex/vorticesupstream from the outlet, i.e. upstream from the outlet aperturededicated to collecting the produced hydrogen.

Indeed, the relative density between the steam and the produced hydrogenin the blend arriving close to the outlet of each elementaryelectrolysis cell is equal to 9 since the molar mass of hydrogen isequal to 2 g·mol⁻¹, whereas that of steam is equal to 18 g·mol⁻¹.

Therefore, by creating one or more vortex/vortices in the flow stream ofthe blend constituted by the produced hydrogen and the surplus steam,both types of molecules (H₂ and H₂O) are subjected to a differentiatedcentrifugal force, which amounts to favouring the centrifugation of theheavy molecules (H₂O) and the extraction of the light molecules (H₂).

This phenomenon of ejection of the steam molecules at the outlet is moreintense the closer it occurs to the outlet.

In FIGS. 2 and 2A the means of creation of the vortices of which theinventor had the idea have been represented in the electrolyserarchitecture, with previously described interconnecting plates 8.

Each interconnecting plate 8 consists of an assembly of two metal plates8.1, 8.2 which have been partially buckled, forming dished recesses inthe form of grooves 80.

As represented in FIGS. 2 and 2A, assembly 8 includes at least oneaperture 84, each of which traverses both the assembled metal plates.

This aperture 84 is made in a zone Z which is dished in a differentmanner to the recesses, at the end of grooves 80. This zone Z which isdished in a different manner to the recesses can be non-dished.

In zone Z which is dished in a different manner at the end of grooves80, holes 83 traverse a single one of the two metal plates 8.1, and areregularly distributed on the periphery of aperture 84.

The diameter of holes 83 is of the order of 1 mm, but it may be less.There is preferably an even number of holes 83, so as to favouralternate rotation of the vortices. Thus, as represented in FIG. 2,there are twelve holes 83 which are regularly spaced around aperture 84.

The assembly of the two metal plates 8.1, 8.2 in differently dished zoneZ delimits a passage 840 between the two metal plates 8.1, 8.2 andbetween holes 83 and aperture 84 (FIG. 2A).

Grooves 80 are the grooves dedicated to the collection of the producedhydrogen. Similarly, aperture 84 is the aperture dedicated to therecovery of the hydrogen produced by the electrolysis reaction: ithabitually constitutes a portion of a collection assembly called asupply manifold, and in which a pierced pipe (unrepresented) isinstalled.

Due to the presence of holes 83 of diameter less than or equal to 1 mm,and to the flow rate at the inlet to zone Z, the blend (surplus steamand produced hydrogen) which arrives in this zone Z passes throughseveral vortices in parallel with tangential speeds of over 100 m/s.

The blend is therefore subject to an acceleration which is calculatedusing the following formula:

$\gamma = \frac{V^{2}}{R}$

-   -   where:    -   γ: Acceleration,    -   V: tangential speed,    -   R: Radius of the outlet hole.

Or

${\gamma = {\frac{100 \times 100}{0.001} = {10^{7}\mspace{14mu} m\text{/}s^{2}}}},$

i.e. an acceleration close to 1 million times terrestrial acceleration.

With such an acceleration the lighter hydrogen molecules tend to beevacuated through holes 83 which are in fluid communication withrecovery aperture 84 (see arrow 15 in FIG. 2A). The water molecules inthe surplus steam, which are heavier than those of hydrogen, for theirpart tend to be ejected towards the outside, and are therefore availableand can be subjected to an electrolytic process in zone Z, i.e. withinthe electrolyser itself.

As represented in FIG. 2, end 800 of grooves 80 upstream from zone Z isadvantageously made such that a jet of hydrogen and steam is created insaid end 800. In addition, at the outlet of this end the jet has a flowwhich is tangential to the axis of each of holes 83. The phenomenon ofvortices created by holes 83 is favoured still further.

FIG. 3 shows diagrammatically the appearance of the stream of hydrogengas V caused by the vortex created by a hole 83, where the arrowsrepresent the injection direction of the water molecules.

FIG. 4 illustrates the increase of the overall efficiency brought aboutby the invention in an EHT electrolyser:

-   -   solid line curve 3 represents the change of the average        production according to the increase of the flow rate of steam        in an EHT electrolyser according to the state of the art,    -   dashed line curve 5 represents the change of the average        production according to the increase of the flow rate of steam        in an EHT electrolyser according to the invention,    -   dotted straight line L_(T) represents diagrammatically the        change of average production according to the increase of flow        rate of steam in the theoretical case in which 100% conversion        of steam into hydrogen is obtained perfectly.

It is clear that due to the invention curve 5 is closer than curve 3 totheoretical straight line L_(T). In other words, the creation ofvortices according to the invention causes a movement towards to a steamconversion rate of close to 100%.

The invention described above therefore consists in creating one or morevortex/vortices in a zone upstream from the recovery zone, i.e. one ormore vortex/vortices tangentially to the axis of the holes for recoveryof the gases produced from the electrochemical reaction, by slowing theevacuation of the reaction gas (H2 in the example), and by tending tosubject the gas or vapour which constitutes the initial constituent(s)to another electrochemical process.

It is stipulated that, compared to the various methods of creation ofvortices in the state of the art used to separate two constituents, inthis case there is a single inlet of gas/vapour and a single outlet ofgas, and the vortex/vortices is/are created tangentially to the axis ofthe reaction gas recovery hole. And, unlike the vortices createdaccording to the state of the art, in which the lightest molecules arerejected towards the outside, in the invention vortices are created toeject the heaviest molecules, i.e. those of the initial constituent(s),to the outside.

The invention described above has many advantages.

Indeed, by incorporating vortex-creation means directly within anelementary electrolysis cell itself, the advantages are as follows:

-   -   increased overall efficiency: indeed, for a given production,        there is no requirement to cause more water to flow, and less        water must be condensed,    -   greater degree of efficiency,    -   simplicity of construction: simple holes to be made within the        high-temperature electrolyser itself,    -   improved compactness due to the fact that less steam must be        made to flow, and to be condensed at the outlet, and this        enables the dimensions of the heat exchangers to be reduced.

Although described with reference to a high-temperature electrolyser,the solution according to the invention is applicable to allelectrochemistry methods in which the reaction gas has a lesser molarmass than the initial constituent(s) in a vapour or gas form, providedthe vortex/vortices according to the invention enable(s) the heaviestmolecules to be separated by centrifugation from the initialconstituent(s) of the reaction gas. The initial constituent(s) are thussubject once again to the electrochemical reaction in the upstream zonein immediate proximity to the outlet from which the reaction gas isrecovered.

For example, in a fuel cell of the PEMFC type, the reaction which occursat the cathode is written as follows:

O₂+4H⁺+4e⁻→2H₂O.

By creating vortices in accordance with the invention at the cathodeoutlet it is conceivable to evacuate the steam produced more easily thanthe supplied oxygen.

1-13. (canceled)
 14. An electrochemistry method to produce a reactiongas of lesser molar mass than that of an initial constituent in a formof gas or vapor, the method comprising: making the gas or vapor of theinitial constituent to flow; and recovering the reaction gas in the pathwherein the initial constituent is made to flow, wherein at least onevortex is created in a zone upstream from the reaction gas recoveryzone, and wherein the vortex can separate the produced reaction gas fromthe initial constituent which is still present, to subject the initialconstituent to an electrochemical process in the upstream zone.
 15. Amethod of high-temperature electrolysis of water according to claim 14,implemented by at least one elementary electrolysis cell formed of acathode, an anode, and an electrolyte inserted between the cathode andthe anode, according to which steam at least, in contact with thecathode, is made to flow from an inlet end to an outlet end, throughwhich end the produced hydrogen is recovered, and according to which atleast one vortex is created in a zone upstream from the outlet end,wherein the vortex can separate the produced hydrogen from the steamwhich is still present to subject the steam to an electrolytic processin the upstream zone.
 16. An electrolysis method according to claim 15at temperatures of between 700° C. and 1000° C.
 17. An electrolysismethod according to claim 15, according to which multiple vortices inparallel with one another are created in the zone upstream from theoutlet end.
 18. An electrolysis method according to claim 15, accordingto which multiple vortices in series relative to one another are createdin the zone upstream from the outlet end.
 19. An electrolysis methodaccording to claim 14, according to which each vortex is created with atangential speed at least equal to 80 m/s, or greater than 100 m/s. 20.An electrolysis method according to claim 14, according to which eachvortex is created to obtain acceleration.
 21. An electrochemical reactorcomprising: a stack of elementary electrolysis cells, each formed of acathode, an anode, and an electrolyte sandwiched between the cathode andthe anode; at least one interconnecting plate fitted between twoadjacent elementary cells, and in electrical contact with an electrodeof one of the two elementary cells and an electrode of the other of thetwo elementary cells, wherein the interconnecting plate delimits atleast one cathodic compartment and at least one anodic compartment forfluids to flow respectively in the cathode and in the anode; and meansto create at least one vortex in a zone upstream from the outlet end ofthe cathodic compartments and/or anodic compartments.
 22. Anelectrochemical reactor according to claim 21, in which the means tocreate the vortex/vortices includes holes pierced in the at least oneinterconnecting plate upstream from the outlet end of the cathodiccompartments.
 23. A reactor according to claim 22, wherein the diameterof the holes is less than 1 mm.
 24. A plate, configured to be used as aninterconnecting plate in a reactor according to claim 21, comprising: anassembly of two partially buckled plates forming dished recesses in aform of grooves, wherein the assembly includes at least one aperture,each of which traverses both assembled metal plates, and made in a zonewhich is dished in a different manner to the recesses, at an end of thegrooves, wherein holes traverse a single one of both metal plates, theholes also being made in the differently dished zone at the end of thegrooves, and being distributed on the periphery of the aperture, andwherein the diameter of the holes is of order of 1 mm or less, and theassembly of both metal plates in the differently dished zone delimits apassage between the two metal plates, and between the holes and theaperture on the periphery of which they are made.
 25. A plate accordingto claim 24, wherein there is an even number of holes.
 26. A plateaccording to claim 24, wherein the end of the grooves is made such thata gas jet or blend of gas and vapor is created in the end, and whereinthe jet also has an outflow tangential to one of the holes.